The present invention relates to an apparatus for measuring such volatile hydrides as diborane (B.sub.2 H.sub.6), arsine (AsH.sub.3), phosphine (PH.sub.3), stibine (SbH.sub.3), hydrogen selenide (SeH.sub.2), monosilane (SiH.sub.4) and the like which are broadly used as doping material or epitaxializer in the field of semiconductor industry.
Hitherto, there have been known methods for measuring the volatile hydride; (1) colorimetric methods (methods of chemical analysis) based primarily upon their reaction with reagents, (2) infrared methods utilizing the property of the gas molecule to be examined to absorb the infrared rays, (3) ultraviolet methods utilizing the property of the gas molecule to be examined to absorb the ultraviolet rays, and (4) atomic absorption method based on measuring the light absorption of the atomic molecule caused by thermal decomposition of the gas to be examined. However, colorimetric methods have such weak points as that the measuring operation thereof is not only complicated but also time consuming. In case of infrared and ultraviolet methods, both of them proved to have poor measurement sensitivity and even concentrations as high as several ppm were hard to be measured by these methods. Further, in the case of atomic absorption method various inconveniences have been experienced; for examples, high temperature on the frame was unavoidable, such apparatus was expensive and the like. As mentioned above none of hitherto known methods for measuring volatile hydrides could bring about a satisfactory result. Further, it has been considered to be extremely difficult or almost impossible to determine extremely small quantities of hydrides by hitherto known method. These compounds being strongly toxic, and the threshold limit value or permissible concentration is generally considered to be as small as about 0.1 ppm, for example; 0.05-0.3 ppm (50-300 ppb), for arsine 0.05 ppm, for phosphine 0.3 ppm, for stibine 0.1 ppm, for hydrogen selenide 0.05 ppm, and for diborane 0.1 ppm, respectively. These compounds were difficult to be detected and measured with accuracy. Especially, diborane has been considered heretofore almost impossible to measure. In view of the fact that volatile hydrides are broadly used these days, the above situation was not desirable for health maintenance.